1. The Field of the Invention
The present invention relates to synthetic water-soluble polymers. More specifically, the present invention relates to water-soluble polymers and crosslinked water-soluble polymers that can be used with methods of selectively removing solutes from a solution.
2. Technical Background
Many solutes are found dissolved in water. Whether the water is a naturally occurring body of water such as lake, stream, river, aquifer, or ocean or a man made body such as process solution sumps, microorganism broths, a mine slag pond, power plant waters, or a municipal waste pond, the water contains dissolved solutes. Some of these solutes are impurities and contaminants that pose a hazard to the environment. Other dissolved solutes may not present a significant health hazard, but affect the taste and quality of culinary water. Yet other dissolved solutes have a significant economic value, which would encourage one to recover the solutes from the solution. The solutes can be of an organic or inorganic nature such as metal cations (for example, Cu2+), metal oxyanions (for example, AgS2O3−1), nonmetal small molecules (for example, Si(OH)4), or organic small molecules (for example, pyridine).
In the environment, rivers, lakes, and ground water are frequently contaminated with hazardous dissolved molecules. These contaminants may come from naturally occurring deposits. However, frequently the contaminants originate in waste streams from industrial sites and investigative laboratories. Other man-made sources of water contamination include abandoned mining operations, solid waste disposal facilities, power plant waters, and municipal waste disposal facilities. For the quality of the water in the environment to be improved, the contaminants need to be removed from a waste stream before the stream is discharged into the environment.
Contaminant solutes such as arsenic, barium, cadmium, chromium, mercury, lead, silver, and selenium are pollutants that are regulated by the Resource Conservation and Recovery Act (RCRA). Because these pollutants are covered by RCRA, strict regulations have been created that restrict the amount of these pollutants that may be discharged into the environment or are allowed in drinking water from natural sources. Moreover, the ability of industry to dispose of waste containing these pollutants is greatly limited. Because of these regulations, there is a great need to be able to remove these solutes from aqueous streams.
A variety of methods have been developed for the removal of RCRA pollutants. These methods frequently use harsh chemicals to precipitate the pollutant from the water. Such chemicals can themselves present a hazard to the technicians employing the method and frequently present additional waste disposal issues. Moreover, the reagents and conditions required for such removal methods can be very expensive. In fact the cost of many clean-up operations is the single biggest obstacle to rapid and effective clean-up of contaminated sites. Cost and effectiveness is a major obstacle to process stream treatment.
Recently, Polymer Filtration technology has been developed for removing such metallic contaminants from water. Generally, Polymer Filtration uses a water-soluble solute-binding polymer to bind the target solute contaminant in water. The solution is then ultrafiltered to concentrate the polymer/solute complex, thus separating the target solute from the bulk of the aqueous solution and purifying the solute from other low-binding components in the solution. The polymer contains oxygen, nitrogen, or sulfur groups, which bind to and form a complex with the solute in solution. The soluble polymers might form a guest-host interaction as its form of complex formation. After the complex is formed, the solution is filtered through an ultrafiltration membrane. The ultrafiltration membrane has a molecular weight cutoff (MWCO) value that is selected to retain the water-soluble polymer and any polymer-solute complex while allowing the water and other dissolved molecules to pass through. This filtration creates a concentrated solution of the polymer/solute complex, which can be more easily treated.
Polymer Filtration technology (PF) has many advantages over other methods of removing solutes from aqueous streams. The major advantage of PF is that the binding of the solute occurs in a homogenous environment, which gives rapid kinetics of binding and can translate into a relatively economical process. The solutes can generally be stripped from the soluble polymer allowing the polymer to be recycled for additional rounds of solute binding. The recycling of the polymer significantly reduces the cost of the removal process because the reagents may be used multiple times. Moreover, because the polymer is recycled, less secondary waste is created, which reduces or eliminates disposal issues. The soluble polymers are generally harmless to the environment, which allows the method to be used at sites of large scale contamination. Polymer Filtration also works with dilute solutions at a variety of temperatures thereby eliminating the need for closely controlled reaction conditions.
Pollutants are not the only solutes dissolved in solutions. Frequently, valuable metal ions may be found in dilute solutions. Because the cost of recovery of metal ions is very high, it is often not economically feasible to recover the metals from solution. Thus, a large amount of potentially valuable materials are lost to aqueous stream. Other solutes such as boric acid and silicic acid are frequently found in solutions. Other dissolved solutes may include inorganic acids and bases as well as organic molecules. Polymer Filtration may be useful to recover or remove these solutes if selective water-soluble polymers were available to bind them.
Other solutes that can contaminate waste streams are acids, bases, and neutral organic molecules. Such acids may be organic acids including diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), imidodiacetic acid (IDA), and ethylenediaminetetraacetic acid (EDTA). Nonmetallic, inorganic acid contaminants may include phosphorus acid, phosphoric acid, boric acid, silicic acid, arsenous acid, arsenic acid, silicic acid, and selenic acid. Bases may include ammonia, and organic amines such as pyridine, methylamine, and dimethylamine. Neutral contaminants include alcohols, aldehydes, nitrites, and amides as examples. Polymer Filtration may be useful to recover these solutes and other solutes of value if soluble polymers were available to bind them.
There may be situations where small molecules have contaminated a surface such as in a radiological contamination or toxic organic chemicals contamination. An aqueous solution of the water-soluble polymer could be used to clean, decontaminate, or deactivate the material from the surface. Or there might be solids that are composed of valuable materials where it might be desirable to leach the valuables from the solid. In these cases the small molecules or ions are extracted into the aqueous solution and bound by the water-soluble polymer and then the solute-polymer complex can be concentrated using ultrafiltration. The solute could be recovered from the polymer in concentrated form and the soluble polymer reused for further cleaning. Or if the soluble-polymers are deactivating the toxic or hazardous contaminate, it might be more desirable to not reuse the polymer, but just stabilize the concentrate.
Other aqueous solutions may contain dissolved solutes that need to be recovered. Such aqueous solutions may be reaction solutions in which useful compounds are synthesized. Such small molecules may include drugs, food additives, pesticides, pharmaceuticals, and the like. Frequently these chemicals are produced in low yield solutions with other reaction products. Therefore, the compound must be concentrated and purified before it can be used for its intended purpose. Such purification methods may be expensive and slow. Also, the purification method itself may create additional byproducts that must be destroyed or otherwise disposed of.
Other useful solutes are produced in aqueous solutions such as growth media from a bioreactor or serum, blood, urine or other bodily fluids from an animal. These small molecules can include polypeptides, nucleic acids, antibodies, drugs, and the like. Like chemically synthesized small molecules, these molecules must be concentrated and purified prior to use. The currently available purification methods for these types of small molecules can be very expensive. Additionally, purification methods frequently use harsh chemicals and conditions, which may result in damage to the useful small molecule or to the bioreactor components. Furthermore some methods of purification are not able to selectively distinguish between a desired product and an unwanted byproduct or other contaminant. Polymer Filtration may be useful to recover these solutes if polymers were available to bind them.
Other aqueous streams that contain solutes requiring recovery or removal are radioactive process streams that come from actinide reprocessing, nuclear power coolant waters, nuclear power reactor wastes, coal power plant waste-waters, and other operations that product waters containing radioactive solutes. The solutes can consist of species such as uranium, plutonium, americium, neptunium, curium, thorium, technetium, radioactive active cobalt, silver, antimony, iodine, and other potential activation products.
There may be some situations where Polymer Filtration technology cannot be incorporated into a separations process. There may be cases where the same solute selectivity that was developed for the soluble polymers is needed in an insoluble form. Then the soluble polymer can be in a crosslinked form and used as a solid gel or resin. Though the solute selectivity may be retained, the rapid kinetics of a homogenous binding system would likely be lost as a two-phase system (water and solid polymer) is established. Cross-linking agents can include a variety of bifunctional agents such as dihalogen alkanes (e.g., 1,2-dibromoethane), dialdehydes (e.g., gluteraldehyde), dienes (e.g., 1,3-butandiene), diepoxides (e.g., diglycidol) and the like. Other modes of crosslinking can include radiation treatment producing radicals that allow the large soluble molecules to bind together forming insoluble polymers.
In light of the foregoing, it would be an advancement in the art to provide new functionalized polymers for use in removal of solutes from water through Polymer Filtration methods. It would be an additional advancement if the polymers had functional groups capable of binding solutes at varying pH levels. A functionalized polymer that could bind RCRA metal ions such as arsenic, barium, cadmium, chromium, mercury, lead, silver, and selenium, and other metal ions such as actinides, fission and activation products, and transition metals would provide significant advancements in clean-up of water contamination. A functionalized polymer that could bind other solutes such as boric acid, silicic acid, organic molecules, and inorganic acids and bases would be a further advancement. An additional advancement would be achieved if the functionalized polymer were able to bind to valuable molecules in dilute solutions. It would be a further advancement to provide polymers capable of binding to anionic solutes or cationic solutes. It would be a further advancement to provide functionalized polymers, which could bind solutes by an interaction other than ionic bonding.